In effecting a fluid seal between a stationary member (such as a wall or housing) and a rotating member (such as a shaft passing through an opening in the wall or housing), it is common to bridge the rotating and stationary members with a sealing member in contact with both to block the leakage of any substance through the opening in the wall or housing through which the shaft passes. Usually, the sealing member is secured to one of the bridged members (either the rotating member or the stationary member) and makes rubbing contact with the other member. With this arrangement, the seal continuously acts as a barrier to the passage of material (either into or out of the housing or through the wall) through the shaft opening.
It is essential that the sealing member maintain continuous contact with both the stationary member and the rotating member if continuous sealing between the two members is to be effected. Although the contact of the sealing member with the member to which it is secured presents no particular problems, the continuous rubbing contact of the sealing member with the other member produces rapid wear which, eventually, will render the sealing member ineffective to perform its sealing function. With such continuous rubbing contact of the seal member, frequent inspection, and periodic replacement, is necessary to avoid leakage.
Sometimes, of course, it is necessary to provide a continuous contact-type seal because the fluid which it is necessary to block is continuously present. However, there are other applications where the fluid which it is desired to block is present only on infrequent occasions. For example, many ships are divided by bulkheads into water-tight compartments. Rotating shafts of the ship's machinery frequently extend through two or more compartments and, accordingly, must pass through openings in the bulkhead separating two compartments. Ordinarily, there is no fluid in either compartment, and sealing is not necessary under normal conditions. It is necessary, however, to seal the openings around the shaft to prevent leakage of water from one compartment to the next in the unusual event that one compartment becomes flooded.
In order to eliminate the continuous wear caused by the continuous rubbing of a sealing member, it is known to provide a seal between a stationary member and a rotating member in which the sealing member is mounted on one of said members and normally out of contact with the other of said members, and in which the sealing member contacts said other of said members in rubbing engagement only in the infrequent event that fluid attempts to penetrate the seal.